Method and apparatus for forming microstructures on polymeric substrates

ABSTRACT

Methods and apparatus for forming microstructures in the surface of polymeric web materials for use as optical memory substrates. The microstructures may be formed by laminating a hot stamper to a web of material with a selective time/temperature profile. The stamper may be heated to melt flow the surface of the web and stabilize before separation. The stamper may be carried by a support that is independent of the press. The web of polymeric material may be provided with a flow enhancer to improve image formation. Also described herein are methods and apparatus for making optical memory modules, such as disks, which include novel stampers, coating applicators, and finishing systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention relates to, and is entitled to the benefit of theearlier filing date and priority of, U.S. Provisional Patent ApplicationNo. 60/300997, filed Jun. 26, 2001, the disclosure of which is hereinincorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to methods and apparatus formaking optical memory. More particularly, the present invention pertainsto forming substrates for optical memory and for making optical disksusing continuous feed or roll-to-roll systems.

BACKGROUND OF THE INVENTION

Optical memory disks, such as CD (compact disks), CD-R, CD-RW; DVD(digital versatile disks), DVD-R, DVD-ROM, DVD-RAM, DVD+RW, DVD−RW, PD(phase change disks) and MO (magneto optical), etc., are typicallymanufactured by initially forming a substrate and then depositing one ormore thin film layers upon the substrate. Substrates for optical memoryare usually formed with a series of grooves and/or pits arranged asconcentric tracks or as a continuous spiral. The grooves and pits may beused for things such as laser beam tracking, address information,timing, error correction, data, etc. Substrates used for optical disksare typically formed by injection molding, where a molten polymericmaterial is injected into a disk shaped mold with one surface having thepatterned microstructure to be replicated. The patterned microstructureis typically provided by an exchangeable insert, commonly referred to asa stamper. The injection molding process is comprised of a series ofprecisely timed steps, which include closing the mold, injecting themolten polymer, providing a controlled reduction in peak injectionpressure, cooling, center-hole formation, opening the mold and removingthe replicated disk and associated sprue. Following the molding process,disk substrates are typically coated with one or more thin film layers.Thereafter, substrates may be coated with various insulating and/orprotective layers, bonding adhesive, decorative artwork, labels, etc.

Although injection-molding methods, such as those described above, canprovide high quality optical memory disks with acceptable levels ofbirefiingence and flatness, the rate of disk production is only in theneighborhood of several seconds. About 60% of this time is attributableto the molding step, and the rest is taken up by the need to open themold, remove the disk and sprue, and then close the mold before the nextcycle can begin. Furthermore, present attempts to improve productionrate by using various novel de-molding techniques or by usingmulti-cavity molds have had only limited success.

Besides lower than desired production rates, injection molding requirescomplex closed-loop control over numerous parameters. For example, moldand polymer temperature, press clamp force, injection profile and holdtime all have competing and often-opposed influences on birefringence,flatness, and on the accuracy of the replicated features. It should alsobe noted that molding difficulty increases as the thickness of thereplicated disk decreases. So where standard CD substrates, which areapproximately 1.2 mm thick, do not require the use of specializedtechniques, such as increasing the molding cavity cross-section duringthe main injection phase, injection-compression molding, coining, “bumpmolding”, etc., standard DVD substrates, which are approximately 0.6 mmthick, do in order to simultaneously meet birefringence and flatnessspecifications.

The trend in future optical memory products is toward thinner substratesand/or smaller disks. Directly manufacturing these products viainjection molding may not be practical.. For small diameter disks (i.e.5-8 cm.), such as the ones used in Personal Digital Assistants (PDA's)and Digital Electronic Cameras, disturbances caused by center gating caninfluence the quality of the innermost tracks on the disk. Thesedisturbances are associated with local turbulence, shear, and packingvariation near the center gate in the mold and can produce locally poorflatness and high birefringence. As the minimum track diameter isreduced, these problems may be exemplified.

To speed-up the rate of manufacturing, a number of methods formanufacturing optical memory using continuous web processes have beenproposed. These methods are built on the concept of forming amicrostructure pattern on a continuous web of material by passing theweb between a roller and a stamper.

To date, there have been two types of continuous web processes proposed.These processes include “in-line” and “off-line” methods. In-linecontinuous web processes integrate web extrusion with microstructurepattern formation in the same process, while off-line continuous webprocesses carry out web formation on pre-fabricated web material whichis manufactured on another production line. The goal of in-lineformation is to contact the web with a stamper immediately after webextrusion and while the web is still hot. Examples of in-line processesinclude those described in U.S. Pat. Nos. 5,137,661; 4,790,893;5,433,897; 5,368,789; 5,281,371; 5,460,766; 5,147,592; and 5,075,060,the disclosures of which are herein incorporated by reference. Theintegration of web extrusion and web formation requires that a diskmanufacturer not only engage in the business of producing optical disksbut also in web extrusion. This makes the overall system a highlycomplex process, at a point in the process where it may not bedesirable. Furthermore, because the disk manufacturer may not enjoy thesame economies of scale that a plastic web manufacturer does, the costper unit for disks formed with in-line processes may be higher than thatfor off-line processes. Thus, the present inventors propose thatoff-line processing not only offers the opportunity for improvedthroughput, reduced cost and complexity, and shorter start-up time, butfor increased process flexibility as well.

One method of web formation, which may be used for in-line processes foroptical memory production, is proposed by Kime, U.S. Pat. No. 6,007,888,entitled “Directed Energy Assisted In Vacuo Micro Embossing” whichissued Dec. 28, 1999, the disclosure of which is herein incorporated byreference. Kime discloses a continuous manufacturing process usingdirected energy assisted micro embossing. The patent describes adirected energy source used to heat web material and a stamper beforethey are pressed together by a pair of nip rollers.

Although Kime is well regarded for what it teaches, when increasinglyhigher density data devices are formed, a number of factors not normallyat issue arise. For example, the preset inventors have found thatunavoidable variation in web surface texture and web thickness exist andcan interfere with fine microstructure reproduction. These variationsresult in locally, non-uniform contact pressure between the web andstamper. In a process where the web is softened to form themicrostructures, simply increasing the average contact pressure fails toadequately solve this problem, as excessively high contact pressure mayresult in a distorted image of the surface due to elastic rebound withinthe web material after. pressure is removed. Stamper web relativemovement can also cause ‘smearing’. Smearing distorts the shape of thedata tracks and/or pits on a microscopic scale. These distortions caninterfere with tracking and can also increase read-back error rates.Accordingly, there is a need for a method and/or apparatus, whichaccommodates the negative effects produced by variations in web surfacetexture and web thickness.

In order to accurately replicate stamper microstructure, many have triedto keep the. stamper in contact with the web long enough for thedisplaced polymer to relax and the substrate cool. However, it was foundby the present inventors that simply increasing contact time is not anacceptable solution due to the resultant increase in warp. As may beappreciated, a warped disk produces significant read problems. Warprelated problems become even a greater problem with writeable disks,where the quality of the recording can be degraded and compounds thedetrimental influence of warp during read-back. Accordingly, there is aneed for a continuous method for producing optical memory and/orapparatus which limits warp during substrate formation.

SUMMARY OF THE INVENTION

In response to the foregoing issues, the present invention provides amethod and/or apparatus for the continuous manufacturing of opticalmemory or optical memory substrates, and/or optical disks which includessupplying a web of material to a substrate forming apparatus.

In one aspect of the present invention there is provided a method forforming polymeric material by limiting the thermal load to the web.

In another aspect of the present invention there is provided a methodfor forming polymeric material by melt forming microstructures on thesurface of a web of material.

In another aspect of the present invention there is provided a method offorming microstructures on the surface of polymeric material with aninductively heated stamper.

In another aspect of the present invention there is provided a method offorming microstructures on the surface of a web of polymeric material byproviding a web of polymeric material with a surface having a flowenhancer; and forming microstructures on the surface of the polymericmaterial with a heated stamper.

In another aspect of the present, invention there is provided a methodof making a stamper for use in a continuous web forming process whichincludes providing a stamper with a transferable image; curving thestamper; and increasing the thickness of the stamper after it is curved.

In another aspect of the present invention there is provided a method offorming polymeric material by providing a stamper with limited thermalexpansion/contraction during web formation. In a preferred aspecthereof, the stamper has a lower coefficient of thermal expansion thannickel. In another preferred aspect hereof, the stamper has a limitedtemperature change during contact with the web.

In another aspect of the present invention there is provided anapparatus for forming microstructures on the surface of polymericmaterial which includes:

-   -   a web feed; a device for web forming, the device for web forming        having a stamper and a set of nip rollers which form a nip zone        in communication with the web feed, the stamper being carried by        a support that is detached from the nip rollers.

In another aspect of the present invention there is provided anapparatus for use in making optical memory which includes: a web feed; astamper for forming polymeric material, the stamper being carried on aloop and in communication with the web feed; a web cutter for sectioningweb material after forming; and a collector for accumulating forsections of web material after cutting.

In another aspect of the present invention there is provided a method offorming microstructures on the surface of polymeric material for use inoptical memory which includes the steps of: providing a roll ofpolymeric web material with a removable layer of softer material; andforming the web with a heated stamper; and re-rolling the formedpolymeric material.

In another aspect of the present invention there is provided anapparatus for use in making optical memory which includes: a web feed; astamper for forming polymeric material, the stamper being carried on aloop and in communication with the web feed; a web cutter for segmentingweb material after forming; an accumulator for receiving sections of webmaterial after cutting; an indexer for making registration holes insections of web material; a masking station for covering sections of webmaterial after forming; and at least one coating applicator for applyingthin film to sections of web material after masking.

In another aspect of the present invention there is provided a websectioning station for use in making optical memory from a continuousweb process which includes: a platform for supporting sections of formedweb material; a plurality of optical positioning sensors for centeringthe image of formed web material on a die path; and a die for cuttingweb supported on the platform.

In another aspect of the present invention there is provided a method offorming polymeric material for use in optical making memory by providinga nip zone with enough compliance so as to take into considerationvariations in the surface and the thickness of the web.

In another aspect of the present invention there is provided a method offorming microstructures on the surface of polymeric material for use inoptical memory, which includes the steps of: providing a web ofpolymeric material; providing a heated stamper; and pressing the heatedstamper and the substrate between a set of nip rollers, wherein at leastone of the nip rollers has a compliant outer surface with a hardness of80 shore D or less.

In another aspect of the present invention, there is provided a systemfor making optical memory disks, which includes one or more of thefollowing: a coating(s) applicator(s), a web cutting device(s), acassette accumulating device, a web indexer, a take-up roll, and othercomponents which can produce a finished optical memory disks or apartially finished disks.

In another aspect of the present invention there is provided a methodfor coating embossed optical memory substrates by masking sections ofweb material prior to coating.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to assist in the understanding of the various aspects of thepresent invention and various embodiments thereof, reference is now bemade to the appended drawings, in which like reference numerals refer tolike elements. The drawings are exemplary only, and should not beconstrued as limiting the invention.

FIG. 1 is a perspective view of an apparatus for forming web materialfor use in optical memory in accordance with the present invention;

FIG. 2 is a perspective view of another apparatus for forming webmaterial in accordance with the present invention;

FIG. 3 is a graphical view of a Time vs. Temperature profile for websurface, melt forming in accordance with the present invention.

FIG. 4 is a side, plan view of an apparatus for forming web material inaccordance with the present invention;

FIG. 5 is a side view of a continuous web, optical memory productionline in accordance with the present invention;

FIG. 6 is a side view of a system for coating optical memory substratein accordance with the present invention;

FIG. 7 is a side view of a system for finishing optical memory inaccordance with the present invention;

FIG. 8 is a perspective view of a system for finishing optical memoryproduction in accordance with the present invention;

FIG. 9 is a side view of a system for holing web material in accordancewith the present invention;

FIG. 10 is a side view of a system for optical memory production inaccordance with the present invention;

FIG. 11 is a top, plan view of a system for finishing optical memory bymasking in accordance with the present invention;

FIG. 12 is a side view of a system for coating web material inaccordance with the present invention;

FIG. 13 is a perspective view of a stamper surface and a web surfaceafter embossing in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made in more detail to the various aspects and severalembodiments of the present invention(s).

Referring now to FIG. 1, depicted therein is a device for formingoptical memory in accordance with the present invention. The deviceincludes a web payoff device, or simply a web payoff (not shown), a webpath in which web material 12 travels, and a web forming apparatusdisposed in the web path. The web forming apparatus 10 includes astamper 14. The stamper carries a microstructure image for forming web.The stamper is carried by a support 28 and may be heated by any suitableheating device 18 and/or may also be heated by a drum or roller 22 inthermal contact with the stamper.

A pressure roller 20 and a backing roller 22 may be disposed in the webpath to press the stamper into the surface of web material. The pressureroller and the backing roller form a nip zone 16. As shown, the nip zone16 includes the narrowest region between the pressure roller 20 and thebacking roller 22. In practice though, the nip zone 16 may be providedby any means suitable for pressing the stamper and the web materialtogether.

The stamper is any tool suitable for leaving an impression in webmaterial or optical memory substrate. The stamper is preferably a diskshaped embossing tool, although in alternative embodiments the stampercould have any shape, such an oblate disk, oval, rectangle, triangle,irregular, etc. The stamper preferably has fine features for producingmicrostructures in optical memory substrates, such as grooves and/orpits. The fine features may range from greater than several microns to0.01 microns or less in width, length and depth. FIG. 13 shows an AFMmagnified perspective view of a stamper surface having fine features anda web surface which has been embossed with the hot stamper toincorporate the fine features into the surface of optical quality webmaterial.

The stamper is preferably formed of a rigid material that can be heatedto a peak process temperature while maintaining the ability to both forma microstructure on the surface of the web and to easily transfer energyto the interface between the stamper and web of polymeric material uponcontact. Representative stamper materials include, nickel, chrome,cobalt, copper, iron, zinc, etc., and various alloys of these metals.The stamper may be composed of a single monolithic material, or ofmultiple layers of the same material or of different materials. Thestamper is preferably comprised of a 0.1 to 1.0 mm thick plate ofmaterial, and is more preferably is comprised of an approximately 0.3mm±0.1 mm thick plate of material. As shown in FIG. 1, the stamper isflat. It is also appreciated that in alternative embodiments, thestamper may be curved. A curved stamper allows the stamper to easilytravel a curved path, such as a repeating loop on a drum, which isparticularly useful for a continuous process.

In a preferred embodiment of the present invention, a curved stamper ispreferentially formed to reduce elliptical image distortion. It has beenfound that simply bending a flat stamper to the shape of a carrier ordrum can introduce elliptical distortion along the direction ofcurvature. The amount of ellipticity is related to the radius ofcurvature (for example, the radius of the drum or path of travel) andthe thickness of the stamper at the time it is curved. It has also beenfound that stretching, compressing-and/or elastically displacing the webmaterial introduces image distortion which must be compensated for. Auseful stamper preferably has micro-structural images with optimallycompensating distortion so that the stamper is suitable for use inmaking optical memory disks. A curved stamper with optimallycompensating distortion may be made by any suitable method, such as byaltering the initial shape of the image and then forming the alteredimage on a curved stamper. However, to take advantage of currentproduction systems for making flat stampers, a curved stamper ispreferably made by imaging the optimally compensating microstructurepattern on a thin, flat stamper, then curving the stamper. After thestamper is curved, the thickness of the stamper is increased to bringthe curved stamper to the desired thickness. By curving and thenincreasing the thickness of the curved stamper, the stamper may bepreferentially formed to optimize image pre-distortion when used with acurved carrier while still meeting the necessary thermal and mechanicalrequirements. For example, an optimally compensating microstructurepattern is formed on a relatively thin workpiece (such as 0.1 mm or lessin thickness). The relatively thin work piece is then curved to adesired radius of curvature (such as 1-10 inches and more preferably 1-5inches) and then built up to the desired stamper thickness. Thethickness of the curved stamper may be built-up by any suitable method,such as plating, bonding, soldering, coating, etc. The final stamperthickness is preferably 0.2 mm or greater and more preferably about 0.3mm. The stamper thickness is preferably built-up on the back of thestamper, e.g. the side opposite the microstructure side. Forming thework piece to the shape of the curved carrier while it is relativelythin directly reduces undesired bending distortion on the image side ofthe stamper surface. Subsequent material addition to the rear surface ofthe pre-curved stamper permits mechanical and thermal characteristics tobe changed without concern about excessive bending distortion.Additionally, in embodiments where the stamper is formed to be used witha curved carrier, a layered construction may additional provide otherbenefits, such as reduced distortion of the stamper upon heating andcooling or by changing the blank side to influence the lubricity of thestamper/drum interface as discussed in more detail herein below.

It has been found that image ‘smearing’ can occur from a differentialmotion between the stamper and the web during embossing. The presentinvention addresses problems, such as smearing, by providing acontinuous web process for making optical memory, which includes a webforming apparatus adapted for reduced dimensional variation at thestamper/web interface. Although pure monolithic nickel stampers may workin conjunction with one or more of the embodiments of the presentinvention, it has been found that pure monolithic nickel stampers do notnecessarily have optimum thermal expansion/contraction characteristics.Further, heat transfer from the stamper to other components of the webforming apparatus can have an impact on stamper contraction. Therefore,a preferred web forming apparatus provides limited thermal contractionof the stamper during contact with the web. In a preferred embodimenthereof, the web forming apparatus is adapted to provide less than 0.5%,more preferably less than 0.1% and more preferably less than 0.01%stamper contraction during web contact.

In a preferred embodiment hereof, stamper dimensional variation islimited by providing the stamper with a coefficient of thermal expansion(and contraction) substantially matched to the thermal response of thestamper/web interface. In certain circumstances, particularly when avery hot stamper is contacted to a cooler web or cooler press, thecontact can cause the hot stamper to cool quickly and contract. Thecontraction is so great that image distortion can occur. By adjustingthe thermal expansion/contraction properties of the stamper, reducedstamper/web differential motion upon stamper contact can be provided toimprove image formation. In accordance with a preferred embodimenthereof, the stamper has a thermal contraction less than that of purenickel or that of conventional nickel stampers. Thermalexpansion/contraction is preferably less than 1%, more preferably lessthan 0.1% and more preferably less than 0.01% over web contact. Reducedthermal expansion and/or contraction may be provided by any suitablemeans, such as by forming the stamper from a material having a lowcoefficient of thermal expansion, or by forming the stamper as amulti-layered structure, etc. Reduced thermal expansion may be providedby making the stamper from an alloy, a ceramic, or coating the stamperwith a different material having a low coefficient of thermal expansion.For example, a stamper may be made by coating a conventional nickelstamper with another metal, a metal alloy or a ceramic having a lowercoefficient of thermal expansion. By selecting materials with a lowcoefficient of thermal expansion, a stamper with substantially nomeasurable relative contraction during web contact can be provided.

In another embodiment hereof, stamper dimensional variation may bereduced by limiting heat loss from the stamper to components of the webforming apparatus or the web or both. Heat loss may be limited in anumber of ways including: providing a bias heat to the stamper backingroller; insulating the stamper from press components; and reducing thestamper contact time with the web. Particularly when the stamper isindependently heated from the press or backing roller, heat can be drawnfrom the stamper into the backing roller to cause contraction of thestamper. By providing a bias heat to the stamper backing roller, heattransfer from the stamper can be limited to reduced thermal contractionof the stamper. Alternatively or additionally, the stamper may bethermally insulated from the backing roller. The stamper may bethermally insulated from the backing roller by any suitable means, suchas coating the stamper with an insulator, coating the backing rollerwith an insulator, etc. Preferably heat loss from the stamper to thestamper backing roller is less than 50%, more preferably less than 10%,and more preferably to less than 1%.

It has been found that by decreasing the time of contact between theheated stamper and the web, reduced dimensional variation can beachieved by limiting heat loss from the bulk of the stamper. Thedecrease in stamper temperature or stamper bulk temperature ispreferably 50° C. or less, more preferably 25° C. or less and morepreferably 10° C. or less. Decreased contact time may be effected byincreasing the speed of the web and/or increasing the speed of the loopon which the stamper is carried. However, it may be beneficial to alsoincrease the amount of heat carried by the stamper when increasing speedso as to carry enough energy to melt flow the surface of the web asdesired. The longitudinal (web motion direction) contact of the web withthe stamper in the nip zone is preferably short in both length and time.The web preferably travels at a rate of 3 to 30 inches per second. Thecontact time between the stamper and the web is preferably 300milliseconds or less, and more preferably 20 milliseconds or less. Thecontact time is most preferably 10 milliseconds or less, but ispreferably greater than 0.5 millisecond. Particularly when the stamperand web are pressed together in a nip or nip zone, the length oflongitudinal contact is preferably 20 mm or less, and more preferably 5mm or less. By limiting contact (such as the length and/or time) of theweb and the stamper, reduced substrate warp may be realized.

The stamper can be carried through the nip zone by any suitable means.Referring again to FIG. 1, the stamper 14 is carried through the nipzone 16 by a support 28. The support may be a web, sheet, chain, belt,pallets, “ferris wheel configuration” , carriage, hoop, rails, drum,roll, etc. The support 28 is preferably a closed loop for repeatedlypassing the stamper 14 through the nip zone 16. As shown in FIG. 1, thesupport 28 is a flat sheet. In alternative embodiments, such as thoseshown in FIGS. 2 and 4, the support 28 may be a carriage.

The stamper may be compressed against the web by any suitable press orpressing device. The device for pressing is preferably a set of rollerswhich form a pinch point or nip. The press preferably delivers apressure of 500 PLI (pounds per lineal inch) or less to the stamper/webcontact zone. The nipping pressure is preferably in the range of 50 PLIto 300 PLI.

As shown in FIGS. 1, 2, and 4, the pressure roller 20 and the backingroller 22 provide a nip zone 16 for pressing the stamper and the webtogether. Particularly where the stamper and web are pressed together bya rounded press such as drums, the length of longitudinal contact ispreferably 20 mm or less, more preferably 5 mm or less and morepreferably 1-2 mm. The pressure roller 20 and the backing roller 22 arepreferably drums or rollers constructed of rigid material, such asmetals, alloys, ceramics, etc. The pressure roller 20 and the backingroller 22 preferably have a smooth finish. In a preferred embodiment,the backing roller 22 is coated with a material selected to effect aninfluence upon the time/temperature profile of the stamper/web interface(as described above) and/or to influence the lubricity of thestamper/drum interface, and/or to provide a compliant surface.(asdescribed below). The characteristics of the backing roller shouldprevent debris generation when contacting the stamper. Representativecoating materials include chrome, cobalt, nickel, iron, steel, stainlesssteel, molybdenum, titanium, zirconium, zirconium oxide, siliconnitride, titanium nitride, synthetic diamond (DLC), Teflon or a Teflonfilled matrix of the above or similar materials. The pressure roller 20and the backing roller 22 are preferably rotatable. The rollers may befree rolling or may be rotated by one or more drives 24 and 26. Thedrives 24 and 26 are preferably independent of each other. If thebacking roller 22 is heated with a bias temperature, it is preferablyoperated cooler than the peak process temperature achieved at theweb/stamper interface side of the stamper 14. By actively controllingthe temperature of the backing roller, improved microstructurereproduction may be achieved by limiting the heat transfer from thestamper to the backing roller.

A preferred method of forming web with a stamper and a set of niprollers includes balancing stamper bending distortion against webstretching distortion by increasing nip pressure to counteract down-webstamper bending distortion and decreasing nip pressure to counteractcross-web or web displacement distortion. For example, a 55 shore Dnipping roller is used with an 8″ nip drum having a curved stamper. Byvarying the nipping force between 600 and 900 lbs, one can balanceellipticity between cross-web and down-web to improve image quality.

Although the apparatus disclosed herein may have wide application informing web material of all kinds, the web material is preferably apolymeric material of suitable optical, mechanical and thermalproperties for making optical memory disks. Preferably, the web materialis a thermoplastic polymer, such as polycarbonate, poly methylmethacrylate, polyolefin, polyester, poly vinyl chloride, polysulfone,cellulosic substances, etc. The web material preferably has a refractiveindex suitable for use in optical memory disks (for example, 1.45 to1.65). The web thickness is preferably about 0.05 mm to about 1.2 mm,depending upon the intended application. The web 12 is preferably wideenough for replicating one, two, three, four, or more images across theweb. The web material may contain one or more additives, such asantioxidants, UV absorbers, UV stabilizers, fluorescent or absorbingdyes, anti-static additives, release agents, fillers, plasticizers,softening agents, surface flow enhancers, etc. The web material ispreferably a prefabricated roll formed “off-line”, which may be suppliedto the substrate forming apparatus at ambient temperature or may besupplied to the system at ambient temperature. Supplying the webmaterial in the form of a roll to the system at ambient temperatureallows for greater process flexibility and efficiency.

To form an impression, the stamper is heated with a heater beforecontacting the web. The heater may be any suitable heating device, suchas a directed energy source, inductive heating source, conductiveheating source, radiating heating source, etc., or any combination orequivalent. The stamper is, preferably, independently heated from theother elements of the system, including the nip, web, rollers, etc. Thestamper is preferably heated just before it is carried to the nip zone.Preferably, the backing drum is also heated.

Heating is preferably supplied by an induction heating coil thatproduces direct resistive heating of the stamper. The induction heatingcoil is preferably made with a conductive material, such as copper,aluminum, silver, etc. The induction heating coil may be comprised of aseries of contoured conductors which are coupled to a suitable source ofenergy. The induction heating coil is preferably water cooled. Theinduction heating coil is preferably placed adjacent to the stamper soas to generate resistive heating in the stamper when the inductionheating coil is energized. The induction heating coil is preferablyplaced within 1 mm to 50 mm of the stamper. As the stamper is heated bythe induction heating coil it can be raised to a temperature sufficientto melt flow the surface of the web. The amount and uniformity ofcoupling to the stamper can be selected by adjusting the size andgeometry of the induction coil; by appropriately selecting the materialsof the stamper; and by changing the distance between the stamper and theinduction heating coil. As shown in the FIGS. 1, 2 and 4, the inductionheating coil 18 is disposed up-stream from the replication zone andadjacent to the path of the stamper.

During embossing, web warp can result from excessive shrinkage and/orsub-surface annealing of the web material. Even minor amounts ofsubstrate warp can be problematic for optical memory devices. Thepresent invention contemplates several methods for reducing thelikelihood of warp. These methods include one or more of the following:controlling the stamper/web interface temperature vs. time relationshipas the web moves through the nip zone, shortening the total processingtime at a temperature above the glass transition temperature, Tg, and/orlimiting the depth to which the web is heated above Tg. Web warp mayalso be reduced by altering the web wrap angle, and/or additionallyheating the web on both sides. Each of these methods may be usedseparately of in combination to improve replica image formation and toreduce warp.

In accordance with the present invention, there is provided a method offorming polymeric web substrates by melt flowing the surface of the web.Melt flow formation is a process wherein the surface of the web materialis heated to a melt, displaced and then allowed to stabilize. As may benoted, forming polymeric substrates by interface surface melt flow isdifferent than traditional compression relaxation methods. In melt flow,as the stamper impinges upon the web, the surface of the web is heatedto such a degree that the material melts and locally flows. Thecombination of material displacement and local flow allows the websurface to rapidly and accurately conform to the shape of themicrostructure pattern on the stamper. Before stamper separation occurs,the web surface is allowed to stabilize. In comparison, compressionrelaxation processes use force to distort and displace material for atime, at a temp below the melting or flow temp, that allows forrelaxation of the strain generated in the web by the compressive forces.By using melt flow formation, instead of compression relaxation, thetime needed for image formation can be greatly shorted so as to limitbulk heating of the web.

In a preferred embodiment of a method for melt flow formation, thesurface of the stamper is provided at melt flow temperature (Tf) orabove. Momentarily raising the stamper/web interface temperature to Tfor above allows rapid, stress free formation of the web surface to theshape of the microstructures of the stamper. While the stamper/webinterface should be hot enough to cause the surface of the web to meltand flow, it should not be so hot that the entire cross section of theweb is melted. The web is preferably melt flowed from the interfacesurface down to a depth of 0.2 mm or less, more preferably down to adepth of 0.1 mm or less, more preferably still down to a depth of 0.05mm or less, and most preferably down to a depth of 1 μm or less.Limiting the process thermal penetration depth to a minimum, such as tothe depth of the structures being formed, can minimize sub-surfacedisplacement and subsurface annealing of the material to reducedistortion and warp.

The melt flow time/temperature profile may be provided in a number ofways, including balancing stamper peak temperature with stamper thermalproperties, adjusting the initial temperature and thermal response ofthe web, adjusting the initial temperature and thermal response of thestamper/web interface, and/or altering the thermal characteristics ofthe rollers that form the nip zone. FIG. 3 exemplifies atime/temperature profile of a method of melt forming in accordance witha preferred embodiment of the present invention. As shown, thetemperature of the web surface (y-axis) during embossing is taken overtime (x-axis). Within the contact time, the temperature of the websurface is ramped from near ambient or Tcold (point A of the graph) toat or above Tf (point B of the graph) and is then [quickly] cooled tostabilize the image before the stamper separates from the web.Alternatively, the web may be preheated to above ambient, or to evenabove Tg before contacting the stamper to the web. Preferably the websurface temperature is dropped to Tf or below before the stamperseparates from the web (shown by point C of the graph).

The stamper is preferably separated from the web at an interfacetemperature below the melt-flow temperature of the web (e.g. at atemperature less than Tf). It should be generally noted that interfacecooling rate may be affected by a number of conditions, including:thermal conduction into the web, the thermal characteristics of theweb/stamper interface, thermal conductivity of the stamper, supplyingone or more insulating layers, and by active interface temperaturecontrol. The stamper is preferably separated at a temperature higherthan the glass transition temperature Tg. Due to the low formationstress associated with melt forming, the processed surface of the web isable to maintain its microstructure after separating from the stamperwhile continuing to cool.

Although not desiring to be bound by theory, polymer response to adisplacing force involves a viscous component and an elastic component.At Tf the viscous component dominates, and at Tcold (a temperature belowTg) the elastic component dominates. Above Tg (the glass transitiontemperature) a transition occurs where the increase in free volumeallows rotational or translational molecular motion to take place. Thisfreedom allows molecules to move past one another, causing viscousbehavior to become more dominant. Embossing polymeric material at Ts orTsoft (a temperature below Tf but above Tg) requires substantialrelaxation of strain before stamper separation. In comparison, variousembodiments of the present invention contemplate embossing the disksubstrate at Tf or above, and cooling the stamper/web laminate to belowTf, but not necessarily below Tg, before separation. The optimumtemperature points reached in various embodiments of the presentinvention permit the microstructures in the web to stabilizesufficiently after separation so as to hold their shape, while at thesame time avoiding microscopic and macroscopic distortion related tostamper shrinkage. The melt forming process of the present inventiontends to eliminate polymer relaxation time constraints associated withtraditional “hot embossing” by providing a low viscosity interface atthe stamper. Melt forming also improves process tolerance to webthickness and texture variation by reforming the surface. Melt formingcan also take advantage of the increased surface mobility and rapidre-stabilization of the surface before stamper/web separation. Bycontrolling the time/temperature profile of the stamper/web interface,microstructures on the stamper may be transferred to the web withreduced defects, such as micro-smearing, track shape distortion, andwarp. An additional benefit derived from a short time/high temperaturethermal profile is a limited thermal penetration depth into the webmaterial. A limited thermal penetration can aid in reducing sub-surfaceannealing of the polymer which has been found to be a contributor tototal warp. Faster melt forming can lower the overall thermal loaddelivered to the web. A lowered thermal load can reduce the depth ofthermal penetration. While it is possible to reduce average thermalexposure by modifying the shape of the time/temperature profile toachieve extremely high peak temperature at the surface followed by arapid cooling, this approach may have a practical limit imposed by theinstability of certain polymers to excessively high peak temperature.

Although a wide range of temperature vs. time profiles can be achievedthrough the appropriate selection of materials, excessively high peaktemperature is still undesirable. It has been found that melt flowformation may be more easily provided if the difference between Tf andTg can be temporarily reduced without compromising the bulk physicalproperties of the web polymer. Applicants have discovered that theselective application of a flow enhancer to the surface of the web priorto melt forming may reduce the required melt-forming peak temperaturewithout compromising the bulk physical properties of the web polymer. Toaccommodate increasingly better flow dynamics without the undesiredconsequences of over heating, it has been found that additives to theweb surface or surface region to temporarily enhance flowcharacteristics may be used.

The web material is preferably provided with a flow enhancer. The flowenhancer may be any material or composition added to the web thatprovides enhanced flow characteristics over the basic web material undermelt-flow conditions. The flow enhancer is preferably a substance thateffectively decreases the melt-flow temperature of the surface and/or isa substance that increases the cooling rate of the surface. The flowenhancer is preferably provided in an amount sufficient to reduce thedynamic viscosity of the web at a.given temperature. Flow enhancer ispreferably provided at 0.1 to 1.0% by weight in the surface region ofthe web. Accordingly, the web material preferably has at least enoughflow enhancer to lower Tf below reported values for dry or flow enhancerfree material and is preferably provided in an amount sufficient tolower normal peak process temperature by 5% to 50%. By providing anamount of flow enhancer sufficient to modify the melt flowcharacteristics of the web, improved optical memory qualitymicrostructures can be produced by melt forming.

The flow enhancer is preferably provided on or in the web surface downto a depth. The flow enhancer is preferably provided to a depth of thefeatures being produced or just below the features being produced. Theflow enhancer is preferably provided to a depth of at least 0.003 μm.The flow enhancer may be provided throughout the entire cross-section ofthe web, but is preferably provided to the top 50% or less, morepreferably to the top 10% or less. The flow enhancer is preferablyprovided from the surface to a depth of 1 μm, and more preferablyprovided from the surface to a depth of 3 μm. In a preferredapplication, only the first 1.5 μm of the surface region has flowenhancer.

Water has been found to be a particularly useful flow enhancer. Not onlyhas water been found to be an effective flow enhancer, but water canbeneficially alter the time/temperature profile at the web/stamperinterface by actively cooling the web surface to create an impediment tocontinued heat transfer from the stamper. Further, it is believed thatwater's high heat of vaporization can enhance rapid cooling at thestamper/web interface to reduce image stabilization time. Traditionally,water present in web materials during hot embossing is highlyproblematic, as water trapped in the web can vaporize and create gasbubbles. These bubbles typically form at the interface between the weband stamper, creating concave depressions in the web surface. These gasbubbles in turn degrade the optical quality of the final product.Typical solutions to the water problem have been to either remove thewater by drying the web or by processing the web at relatively lowtemperatures (below Tg). The applicants have discovered that thepresence of water in the surface of the web during melt forming canactually be beneficial, as the right amount of water can not onlyimprove the quality of the microstructures transferred to the web, butcan do so without the formation of water vapor bubbles. Prevention ofdamaging water volatilization may be achieved by providing a shortprocess time with a shallow depth of thermal penetration. Because theefficacy of the melt-forming process is enhanced by the presence ofwater, peak process temperature can be reduced. The reduction in peaktemperature requirements further reduces thermal penetration, therebyresulting in less warp. Water is preferably provided in an amount ofabout 0.1 to 0.4 percent by weight of web material. To provide apreferred amount of water in the surface of the web, moisture may beadded, removed, or both. In some cases, the web may be dried prior toembossing. In other instances, the web may be subjected to a watersurface treatment prior to embossing. In other cases, it may benecessary to surface condition the web by first drying the web and thentreating the pre-dried web with water just prior to embossing.

It is also appreciated that although water is a preferred substance,other flow enhancers may also be used. Other flow enhancers, includeplasticizers, resin emulsions, and release agents that are applied tothe surface or integrated with the surface of the web in proper amounts.Preferred flow enhancers may include one or more compounds selected fromthe chemical families of fatty esters and fatty acids. A preferred flowenhancer includes the fatty ester, pentaerythrithitol tetrastearate. Theflow enhancer may be supplied to the web by any suitable means, such asdipping, coating, spray application, a fine mist, absorption, immersionin a wetter augmented bath, vaporization chamber, addition to theinitial plastic resins, addition to the initial extrusion raw materials,etc. The flow enhancer is preferably applied in a way that provides aneven coating of material on the surface of the web material. Preferablythe flow enhancer provides properties suitable for temporarily loweringeffective web Tf during the melt-forming process, and/or, as a result ofprocess conditions, results in a permanent increase in web surface Tg.

To achieve preferred temperature profiles during web formation, therollers or drums that form the nip zone may be adapted with thermaltransfer properties sufficient to maintain proper heating and cooling ofthe web/stamper interface, such as active or passive heating or cooling.Referring to FIG. 4, the rollers 20 and 22 may be thermally conductiveand provided with an outer layer 21 and an insulator layer 23(respectively) which are selected so that there is just enough thermalinsulation to allow the web surface to cool to below its melt flowtemperature (Tf), but not necessarily below its glass transitiontemperature (Tg), by the time the stamper 14 separates from the web 12.If either the outer layer 21 or the insulator layer 23 is overlyinsulating, the web surface may not cool sufficiently to fully stabilizeby the time the stamper 14 is separated from the web, allowing themicrostructure to change shape. If the outer layer 21 or the insulatorlayer 23 is under insulated, the stamper 14 may cool so much that itshrinks before it comes out of contact with the web, resulting insmearing of the microstructure and distortion of the shape of thetracks.

In a preferred embodiment of a method for forming polymeric webmaterial, the web is also heated on the side opposite that wheremicrostructures are formed, e.g. on the ‘blank side’. Heating on the‘blank-side’ of the web allows for counteracting residual warping forcesfrom post anneal cooling. Heat may be provided to the blank side by anysuitable heating device. Heat is preferably provided by either radiantheat or may be provided to the web by a heated roller configured tocounteract the thermal penetration depth resulting from stamper contact.The blank side of the web may be heated prior to entering the processnip zone, such as by radiant heat or conductive heat, or may be heatedin the process nip zone simultaneously with microstructure formation.The blank side is preferably heated in an amount sufficient to balancesub-surface annealing created on the stamper side. The blank side mayalso be heated in the same way as the stamper is heated, such as byinduction heating. This approach may be extended to effect thesimultaneous melt forming of both sides of the web.

In practice, web material can be delivered to the nip zone by anysuitable web feed means. The means for feeding is preferably a devicesuitable for continuously delivering web material to the stamper alongthe web path, such as a sheet feed, folded material feed, roll feed, webextruder, etc. The web feed is preferably a roll feed, such as one shownat 300 in FIGS. 5 and 9 for feeding pre-manufactured rolls of polymericweb material to the nip zone. The-roll of polymeric web materialpreferably includes a removable film or protective layer of material,such as a softer plastic film layer on the web. By using web having asofter protective layer, the web may be rolled, unrolled; and re-rolledwith minimal to no surface scratching, which could otherwise affect theuse of the web for optical memory devices.

The web feed may be complimented by a web take-up device, such as atake-up roll, for collecting the web after processing or afterformation. Alternatively to using a take-up roll, the web may be cutinto sections after formation (such as described below) or may befurther processed into completed or partially completed optical memorydisks.

The web formation apparatus is preferably adapted to accommodatevariations in web tension so that the web is neither over-taunt norover-slacked. An over-taught web could result in the web breaking whilean over-slacked web could cause jamming or other problems. Furthermore,tension control across the nip zone should be controlled to reducesub-surface material displacement and ellipticity of the reproducedimage. To accommodate variations in web tension, the system may beprovided with one or more tension rollers. Tension rollers are generallyknown in material handling operations and may be used to control webspeed and tension.

Tension may be controlled across the nip zone, at the nip in-feed, atthe nip out-feed, and otherwise across the system. Tension at the nipin-feed is preferably near 0 to neutral. The system may also have one ormore guide rollers (not shown) for guiding the web in the web path, foraltering the angle of the web into and out of the nip zone and forchanging direction of the web. Preferably, there is at least one guideand/or tension roller for directing the web into the process nip zone,and at least one guide and/or tension roller used to direct the web outof the nip zone. These guide and/or tension rollers may serve theadditional purpose of establishing the process nip zone in-feed andout-feed contact and separation angle between the web and stamper. Theguide roller on the side exiting the nip zone preferably allows aninitial web/stamper separation angle of about 900°±1°. The guide rollerpreferably guides the web away from the stamper immediately afterexiting the nip.

Referring to FIG. 1, 2, and 4, the heated stamper 14 is carried into thenip zone 16 by a support 28. The stamper 14 is preferably temporarilylaminated to the web 12 as a result of free float through the nip zone.The support 28 is preferably independent of, or detached from, the niprollers, 20 and 22, and any components thereof. The independence of thesupport 28 may allow the stamper 14 to substantially free float on theweb 12 as it becomes temporarily laminated thereto in the process nipzone 16. By laminating the stamper to the web with an independentsupport, a stamper with more than one degree and more preferably morethan 2 degrees of freedom of movement may be realized. By having morethan one degree of freedom, the stamper 14 can better accommodate andconform to roller pressure-induced distortions within the web 12 duringthe melt forming process and more completely accommodate web texture andthickness variations.

Referring now to FIG. 2, depicted therein is a web forming system inaccordance with a preferred embodiment of the present invention whichincludes a web forming apparatus 10 having a special support thatdecreases the angle in which the stamper enters the nip zone 16. Thesystem includes a web feed 42, a web path 44 in communication with theweb feed 42, and a nip or a nip zone 16 disposed in the web path 44 anda stamper 14. The stamper 14 is carried by a set of “hoops” 118, 128which forms the support that follows the web path 44 through the nipzone 16 and carries the stamper 14 between the pressure and backingrollers, 20 and 22. The support is preferably detached from the pressureand backing rollers, 20 and 22, and preferably results in the temporarylamination of the stamper 14 to the surface of the web 12 in the nipzone 16. As shown, the hoops form a carriage 114 for the stamper to rideon. The carriage 114 provides means for independently carrying thestamper through the nip zone 16. By independently carrying the stamper14 into and through the nip zone, better thermal management of theprocess can be provided. Additionally, by independently carrying thestamper 14 through the nip zone, the stamper may be kept more nearlyflat, thereby reducing ellipticity caused by forming a curved stamper inthe shape of a small diameter carrier drum.

As shown, the carriage 114 is supported around the backing roller 22 ona plurality of rollers 30, 32, 34. The rollers 30, 32, 34, permit freerotation of the rails 118, 128. The stamper 14 may be connected betweenand supported by the rails 118, 128 by any suitable means. The rails arepreferably separated by a distance equal to the width (cross web) of thebacking roller 20 so that only the stamper (as opposed to the rails)contacts the backing roller during operation. The rails 118, 128preferably have a circumference substantially greater than that of thebacking roller 22. The ratio of the circumference of the rails to thebacking roller is preferably at least 5:4, and more preferably a ratioof about 13:8 or greater. Rails with a large circumference may aid inkeeping the stamper flatter through the nip zone 16.

In operation, the backing roller 22 engages the back of the stamper 14to guide the stamper into contact with the web 12 while the pressureroller 20 presses the web into the front of the stamper. The rollersurfaces are preferably selected to provide the necessary contactuniformity, to optimize nip zone dynamic shape and to balance pressuredistribution to minimize overall image distortion. The pressure rollerand/or the backing roller preferably include compliant surfaces. Apressure roller and/or backing roller with a compliant surface canprovide a stamper with enough flexibility so as to accommodate webthickness variations to improve image formation. The compliant materialis preferably between 0.05 and 0.5 inches thick and more preferablyapproximately 0.125±0.1 inches thick. The compliant material 21 ispreferably selected to have a hardness rating of less than 80 shore Dand preferably between 90 shore A and 60 shore D. The backing roller 22may also include a layer of compliant material 23 which may be the sameas or different from (in thickness, compliance, resiliency, lubricity,and/or heat transfer characteristics) the compliant material of thepressure roller. If both rollers have compliant surfaces, the surfacesare preferably adapted such that the combined characteristics optimizepressure and heat transfer uniformity without introducing pressure,shearing, and/or velocity instabilities into the stamper/web laminate.Preferred compliant materials include, but are not limited to, nitrile,EPDM, Kapton, epoxides, filled epoxides, Teflon, and Teflon infusedpolymer, metal or ceramic matrixes. It is also appreciated that anymaterial with compliance and heat transfer properties suitable for meltforming an optical memory microstructure with less than ±0.8 degrees ofradial deviation, and less than ±0.3 degrees of tangential deviation maybe used.

With reference to FIG. 5, a preferred embodiment of a system formanufacturing optical memory media 200 is shown. The system 200 includesa web pay-off 300, web material forming apparatus 10, a coating(s)applicator 400, a web cutting device 500, and a cassette loading oraccumulating device 600. The system 200 may be used to process acontinuous web 12 of material to produce finished optical memory storagemedia, such as optical disks.

As shown in FIG. 5, a roll 310 of web material 12 is provided by a webpay-off device 300. The web material 12 may be of any width andthickness that is useful for manufacturing optical memory substrates.The roll 310 may be interchangeably mounted on a reel 320 contained inthe pay-off device 300. The web material 12 dispensed from the roll 310may be run through one or more guide/tension rollers 330 to the formingapparatus 10.

As various embodiments of substrate forming apparatus have beendiscussed previously, it is appreciated that any of the embodiments ofweb forming apparatus, which have been previously discussed, could beused with the system 200 described herein. The forming apparatus 10receives web material from the web pay-off device 300. The disksubstrate forming apparatus 10 is used to form a pattern ofmicrostructures into the web material. After the microstructures areformed in the web material, the material may be further processed tomore fully complete the manufacture of an optical memory device. Toprocess the web material further, the material may be sent to a coatingapplication 400.

Various coatings may be applied to the web material in either acontinuous manner, such as to the web before sectioning into strips ofweb material, or after sectioning by batch. The coating applicator 400may include one or more coating units 410, 412, etc., used to applycoatings to the web 12. The coating units may be capable of maintaininga vacuum surrounding the web 12 and applying a coating using a one ormore coating processes, such as CVD, PVD, PCVD, PECVD, PML, LML,sputtering, or other deposition process.

Table 1 below identifies example processes, coatings, and coatingthickness that may be used to form desired coatings on phase change,optical memory substrates. TABLE 1 Coating Step Process CoatingThickness (nm) 1 Microwave PECVD Dielectric anti-reflective  60-150 2Sputter Chalcogenide 20-25 3 Microwave PECVD Dielectric 20-25 4 SputterAluminum  60-150 5 PML/LML Acrylate 5,000-7,000

A coating unit 410 may be used to apply a dielectric anti-reflectivecoating in the range of aproximately 500 to 2000 angstroms thick andmore preferably in the range of 60 to 150 nanometers thick. Thedielectric coating may be comprised of any suitable material such assilicon dioxide, silicon nitride, titanium oxide, zinc sulfide, siliconoxide, germanium nitride, geranium oxide, silica, alumina, combinationsof the above, and the like. Preferably, the dielectric anti-reflectivecoating has an index of refraction of about 2.2. For this reason,silicon nitrite, which can be deposited with an index of refraction ofabout 1.9, and titanium oxide, which can be deposited with an index ofrefraction of about 2.3, may be preferred.

Although any type of deposition process may be used to apply thedielectric anti-reflective layer, in a preferred embodiment, microwavePECVD process is used. Examples of microwave PECVD processes and systemsthat may be used for coating include those disclosed in U.S. Pat. Nos.5,411,591; 5,562,776; 5,567,241; 5,670,224; 6,186,090; and 6,209,482,the disclosure of each of which is incorporated by reference herein.Microwave PECVD processes such as those disclosed in theabove-referenced patents may be preferred over other depositiontechniques because of the speed at which the deposition can be carriedout. An increase in deposition rates may also allow a reduction in theoverall length of the deposition chamber required for coating. Reductionin the deposition chamber length can greatly decrease the costsassociated with the deposition process.

A memory layer coating unit 412 may be used to apply a phase changememory material coating. The memory material coating preferably includesa chalcogenide alloy in the range of approximately 4 to 30 nanometersthick, and more preferably approximately 20 to 25 nanometers thick.Although any type of deposition process may be used to apply thechalcogenide alloy coating, in a preferred embodiment it is sputteredonto the web 12.

A second dielectric coating unit 414 may be used to apply a seconddielectric coating in the range of approximately 150 to 2000 angstromsthick, and more preferably approximately 20-25 nanometers thick.Suitable dielectric materials include those described above. Althoughany type of deposition process may be used to apply the seconddielectric layer, in a preferred embodiment, a microwave PECVD processis used.

A coating unit 416 for depositing a reflective or heat dissipationmaterial may be used to apply a thin layer of a metal, such as aluminumor the like, in the range of approximately 1 to 1000 nanometers thick,and more preferably approximately 60 to 150 nanometers thick to thesubstrate. Although any type of deposition process may be used to applyany suitable material coating, in a preferred embodiment the reflectiveor heat dissipating layer is sputtered or evaporated onto the web 12.

A coating unit 418 may be used to apply a protective coating. Theprotective coating is preferably 1,000 to 7,000 nanometers thick. Theprotective coating may be formed of any suitable, optically transparentmaterial, such as a thermosetting resin, uv resin, acrylate, etc. In apreferred embodiment, a Polymer Multi-Layer or Liquid Multi-Layer(PML/LML) process is used to provide the acrylate coating. A PML processinvolves the vacuum flash evaporation of monomer fluids to produce aliquid film condensate, which is then radiation cross-linked to form asolid film. A LML process involves the vacuum coating of the monomerliquid directly onto the substrate by means such as extrusion, gravurerollers, spraying, etc., and subsequently radiation cross linkingmonomers in the thin liquid coating. LML processes may require coatingsin excess of 10 micrometers, and accordingly, PML may be preferred forthe formation of an acrylate coating.

Isolation of the vacuum deposition chambers of each of the coating units410, 418, etc., from each other, from web formation, and from the payoffdevices, may be achieved by any suitable isolation device, such as gasgates, etc.

The materials for and thickness of the two dielectric coatings should bechosen carefully to fulfill several functions in the finished opticaldisk. These dielectric coatings may protect the phase change coatingfrom exposure to oxygen or water vapor, which could oxidize the phasechange material and alter its properties. The dielectric coatings mayalso be used to provide good contrast and to aid the laser beam that isused to “write” on the disk to be absorbed primarily in the phase changecoating. The dielectric layers may also affect the thermalcharacteristics of the optical disk. The second dielectric coatingbetween the phase change coating and the aluminum coating is selected tobe thermally conductive enough to prevent overheating the laser targetedareas of the phase change coating, but not so thermally conductive as toprovide excessive heat loss to the aluminum coating. Finally, thedielectric coatings provide rigid supports for the phase change materialsandwiched between them when it is heated by a laser.

It is appreciated that the above-referenced microwave PECVD processesfor the application of the dielectric coatings may cause build up ofdielectric material on the lens that isolates the microwave source fromthe PECVD chamber. In order to facilitate continuous web processing, aninnovative method that effectively replaces the lens on a continuousbasis has been developed.

With reference to FIG. 6, a web 12 of material used to produce opticaldisks is coated with material in a deposition chamber 440 of a coatingunit 410. The deposition chamber 440 includes an aperture 442. Areel-to-reel web of polyester 420, or other flexible, microwavetransparent material, may be used to shield the lens between themicrowave source 430 and the deposition chamber 440. The microwavetransparent web may be continuously or intermittently drawn from a firstreel 422, past the aperture 442, and onto a second reel 424. Opposingrollers 426, or other means, may be provided to create a seal at theintersection of the aperture 442 and the polyester web 420. Thepolyester web 420 may be repeatedly wound back and forth past theaperture 442 during PECVD operation until the build up of material (suchas dielectric coating material) on the surface 421 mandates itsreplacement. Use of the polyester web 420 to provide the microwave“window” into the deposition chamber 440 may greatly increase the lifeof the window.

The foregoing discussion of the coatings that may be used to produce aphase change optical memory storage device is intended to be exemplaryonly. It is appreciated that the coating system may be used to apply anynumber of different coatings, in different orders, and differentthicknesses, in order to produce a wide variety of optical memorystorage devices, such as those discussed in the background section ofthis application. Accordingly, the detailed discussion of phase changememory devices should not limit the scope of the present application.

Again with reference to FIG. 5, after coating, the web 12 exits thecoating applicator 400 and enters a web cutting or sectioning device500. The web cutting device 500 may be any device suitable forseparating web into sections or strips 510 that are some multiple ofdisks, such as one or more in length or width. The web cutting devicemay include a rotary cutter for sectioning the web. The web cuttingdevice may also include a system for removing dust or debris produced bythe cutter, such as ionized air and vacuum.

After the strips 510 are formed they may be collected or accumulatedinto bins or removable cassettes 610 with an accumulating device 600. Bycollecting disks into an accumulator, line speed can be increased and bycollecting sections of web in removable cassettes, sections of web canbe finished either offline or on multiple lines. Disk finishing may alsobe done directly from the web or from a continuous roll of embossed andcoated material.

Disk finishing requires precise formation of the outer (outer diameter,o.d.) and center portions (inner diameter, i.d.) of the replicatedsubstrate and disk microstructure. Disk finishing may include any of awide variety of operations, such as punching, cutting, milling, or othermeans of forming the i.d. and o.d. of disks.

With reference to FIG. 7, shown therein is a disk finishing system 800in accordance with a preferred embodiment of present invention. The diskfinishing system may be adapted for accepting strips 510 from theaccumulator 610. At the initiation of the disk finishing system, strips510 of web can be unloaded from cassettes onto a conveyor. The stripsmay be conveyed to a rough cut or squaring station 820. At the squaringstation, the strips 510 can be cut into smaller shapes, such as squares822 that contain only a single disk microstructure. After the strips 510are cut into squares 822, the squares may then be conveyed to aseparator ring embossing station 830, where an elevated ridge ofsubstrate material (i.e., a disk separator ring) may be formed. Theseparator ring allows stacked disks to be easily separated when stackedtogether and prevents scuffing damage to the microstructure. Afterformation of the separator ring on the disk substrates, each may be sentto center hole punching or blanking station 840 and then to a scrap(material outside of the disk) removal station 850. After the centerhole and the scrap around the disk are removed, the individual,semi-finished disks may be stacked at a stacking station 852.

With reference to FIG. 8, depicted therein is a preferred web sectioningstation which may include a device 842 for centering the microstructurepattern of a disk substrate. The device 842 may include a table orplatform 844 that is disposed above the web 12 on which the disksubstrate microstructure pattern 13 has been formed. The table 844 maybe selectively translatable in the x and y directions by a motorizedassembly (not shown). Optical sensors 846 may be supported by the tableand directed orthogonally toward the web 12. The optical sensors 846 mayprovide detection signals to a control unit 848. The detection signalsreceived by the control unit 848 may be used to control centering andtranslation of the table 844. The table 844 is translated so that eachof the optical sensors 846 is located directly above the edge of themicrostructure pattern 13 on the disk substrate. Once the table 844 iscentered above the microstructure pattern, a punch unit 860 carried inthe center of the table 844 may be used to form the center hole (i.d.)and/or (o.d.) of the memory device.

A preferred embodiment of a punch unit is shown in FIG. 9 at 860. Thepunch unit 860 may include a staged center die 862, a silicone pad 864,a spring 866, and a die button 868. The die may be constructed of anysuitable material. The die may include one or more stages. Preferably,each stage has a depth suitable for cleanly piercing polymericsubstrate. The spring 866 may be disposed to bias the pad downward toclamp the web 12 between the pad 864 and the die button 868. The stagedcenter die 862 may then be pressed down through the web 12 to form acenter hole therein. The stages formed in the center die 862 can reducethe likelihood of forming a center hole with a jagged or irregular edge.

Referring now to FIG. 10 is an alternative embodiment of a system forforming optical memory 200, in which like reference numerals refer tolike elements shown in the other drawing figures. As shown in FIG. 10,the web pay-off device 300 may include a splicing unit 340 for providingcontinuous web pay off from multiple rolls 310 of web material.

The system, as exemplified by FIG. 10 may be particularly useful for theproduction of optical substrates for DVDs. As noted previously, DVDs areproduced by joining two disks together. The surface of the informationcarrying disk that is bonded to the opposing disk is the same surfacethat may have one or more coatings applied to it. The coatings, however,are not conducive to the formation of a mechanically robust,hermetically sealed bond between the information carrying disk and theopposing disk. Accordingly, there is a need to leave portions of theinformation carrying disk, namely the outer edge of the perimeter andthe inner perimeter, uncoated. As such, a system for masking portions ofthe substrates before coating may be used to form disk substrates withuncoated outer and inner regions which are useful in bonded memorydevices.

In accordance with a preferred embodiment of the system for maskingportions of the substrates before coating, there may be provided anindexing system so that edges of memory devices can be accuratelyformed. Substrate indexing may be provided by one or more pre-punch andpost punch stations, items 900 and 950 of FIG. 10, respectively.Indexing allows accurate disk removal, accumulating and coating of webmaterial.

For example, FIG. 11, shows a disk substrate 13 at various stages offormation, A, B, C, and D, representing the evolution of the disksubstrate as it passes through various processing stations. At stage A,the pre-punch station 900 (FIG. 10) may put a center hole 15 and one ormore registration holes 17 in the web. The center hole 15 may be formedby any means, such as a punch unit as shown in FIG. 9, by melting,drilling, cutting, etc. The center hole 15 may have a diameter that isthe same as or less than the final center hole in a finished opticaldisk. If the diameter of the center hole 15 is less than that requiredfor a finished optical disk, it may be enlarged at a later processingstage. Like the center hole 15, the registration holes 17 may be formedby any means, such as a sprocket punch. The registration holes may ormay not extend entirely through the web 12. Preferably, the center hole15 is precisely equidistant from each of the registration holes 17 sothat the relationship of the registration holes to the center hole isknown.

With continued reference to stage A, after the center hole 15 and theregistration holes 17 are formed in the web 12, the web passes to theweb forming apparatus 10. The forming apparatus 10 may be equipped withmeans for engaging the registration holes 17, such as pegs or keys. Byengaging the registration holes, the forming apparatus 10 can registerthe stamper with the web 12 so that the microstructure pattern ispositioned precisely around the center hole 15.

With reference to stage B of FIG. 11, after the microstructure patternis formed on the web 12, the disk substrate 13 is sent to the post-punchstation 950 (FIG. 10). At the post-punch station 950 a central plug 952may be inserted into the center hole 15. The central plug 952 may beconstructed of any suitable material. The central plug 952 may befastened to the disk substrate 13 in any suitable way. The central plug952 is larger than the center hole 15 so that it masks an innerperimeter region 954 of the disk substrate 19. The masked innerperimeter region 954 is preferably fixed to have a width ofapproximately that of conventional media.

With reference to stage C of FIG. 11, an outer mask 956 may be appliedover the disk substrate 13 while it is at the post-punch station 950.The outer mask 956 may be registered to the web 12 by engaging theregistration holes 17 of the web. The outer mask 956 may be constructedof any suitable material. The outer mask 956 may be fastened to the disksubstrate 13 in any suitable way. The diameter of the interior opening957 in the outer mask 956 is less than the final diameter of the disksubstrate 13, so that it masks an outer perimeter region 958 of the disksubstrate. The masked outer perimeter region 958 may preferably have awidth of approximately ½ to 3 mm, and more preferably of approximately 1mm.

After the plug 952 and the outer mask 956 are in place, the disksubstrate 13 may be conveyed from the post-punch station 950 to the webcutting device 500 where the web 12 can be cut into strips 510 of asuitable length and/or width. The strips 510 may be accumulated forfurther processing by batch or may be immediately transferred to acoating applicator 400. At the coating applicator 400, the strips may beplaced into tracks disposed along the inside cylindrical surface of arotating drum portion 450. The strips 510 may be loaded into the drum450 so that the masked surfaces of the disk substrates 13 are exposed tothe drum interior or coating stream. The drum may be sealed, by anysuitable device during coating.

The drum 450 of the coating applicator 400 may be arranged to rotateorthogonally to the direction of the web 12 pay off. Arranging the drumorthogonally to the direction of the Web pay-off allows web strips 510to be linearly advanced directly into the drum 450. The side of the drum450 opposite the web cutting device 500 may be open to allow one or morecoating units 410 to be inserted therein. The coating units 410 may bemounted on an internal wall capable of being sealed in the drum 450.Once the wall on which the coating units 410 are mounted is closed, thedrum can be rotated about its axis so that the web strips 510 disposedalong the inner wall of the drum are transported through various coatingzones defined by the coating units 410. A side view of the drum 450 andthe deposition chamber 440 defined thereby is shown in FIG. 12. In orderto carry out the coating process with a drum-shaped coating apparatus400, it maybe necessary to cool the drum 450 or the substrate in thedrum. One method of cooling the-drum 450 is to include a waterjacket 460around the outside of the drum. The use of a waterjacket allows controlover the temperature of the drum and over web strips disposed inside ofthe drum.

With continued reference to FIG. 11, after the disk substrate 13 iscoated, the plug 952 and the outer mask 956 may be removed. The disksubstrate 13 then appears as shown in stage D, including coatings on thesurface with the exception of the outer perimeter region 958 and theinner perimeter region 954. The strips web that reach stage D may thenbe sent to a finishing line, such as one discussed above in connectionwith FIG. 7. The finishing station for disk substrates that reach stageD, however, may require an additional station to bond the informationcarrying substrate to an opposing substrate (such as a blank or embossedmaterial).

An alternative embodiment of the drum-shaped coating apparatus 400 is tohave the coating apparatus 400 rotate in line with the web pay offdirection. As a result, the disk substrates, in strip or web form, maybe loaded directly onto the drum 450 as it rotates.

The embodiments of the invention(s) disclosed heretofore may be usedwith or without melt forming. While melt forming contemplates formingmicrostructures into the surface of the web during a very brief periodof time (on the order of tens of milliseconds, preferably less), severalof the embodiments of the preceding may be useful with other replicationprocesses. While the invention has been illustrated in detail in thedrawings and the foregoing description, the same is to be considered asillustrative and not restrictive in character as the present inventionand the concepts herein may be applied to any formable material. It willbe apparent to those skilled in the art that variations andmodifications of the present invention can be made without departingfrom the scope or spirit of the invention. For example, the dimensionsof the optical substrates, and the microstructures formed therein can bevaried without departing from the scope and spirit of the invention. Thematerials used to construct the various elements used in the embodimentsof the invention, such as the pressure and backing rollers, the stamper,the stamper support, and the heater, may be varied without departingfrom the intended scope of the invention. Furthermore, it is appreciatedthat the support for the stamper and the backing roller could beintegrated so as to provide one structure. The stamper may then beseparated from the backing roller with an insulator. Still further, itis appreciated that the present invention extends to embodiments thatuse optical memory substrates in any form, be that web, sheet, orotherwise. Further more, by using one or more of the embodimentsdescribed above in combination or separately, it is possible to makeoptical memory disks with less than ±0.8 degrees radial deviation, andless than ±0.3 degrees tangential deviation, with a birefringence ofless than 100 nm double pass, more preferably less than 90 nm doublepass, and still more preferably less than 60 nm retardation, doublepass, through 1.2 mm, or less, of web material. Thus, it is intendedthat the present invention cover all such modifications and variationsof the invention, that come within the scope of the appended claims andtheir equivalents.

1. A method of making a stamper for use in a continuous web formingprocess comprising the steps of: providing a stamper with a transferableimage; curving the stamper; and increasing the thickness of the stamper.